Recoil and conversion electron implications to be taken into account in the design of therapeutic radiopharmaceuticals utilising in vivo generators

Jan Rijn Zeevaart, Zoltan Szucs, Sandor Takacs, Johann Van Rooyen, David Jansen

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

The use of radionuclides as potential therapeutic radiopharmaceuticals is increasingly investigated. An important aspect is the delivery of the radionuclide to the target, in which the radionuclide is not lost from the chelating agent. For in vivo generators, not only the log K of complexation between the metal ion and the chelator is important but also whether the daughter radionuclide stays inside the chelator after decay of the parent radionuclide. In our previous work, we showed that the classical recoil effect for β-decay only applies to decays with a Q value higher than 0.6MeV (for the atomic mass range around 100). However, the published result for 140Nd/ 140Pr (Q=0.222MeV) indicated that >95% of the daughter ( 140Pr) was lost by a DOTA chelator upon decay of 140Nd. The experiment was repeated with the 166Dy/ 166Ho generator (Q=0.486MeV) and the 90Sr/ 90Y generator (Q=0.546MeV), which resembles an in vivo chelator system where the transition via the Auger process is absent. It was found that 72% of the daughter ( 166Ho) was liberated from the DOTA chelator, in contrast to our recoil calculations. It was also found that this ratio of the 166Ho released corresponds to the ratio of transition of holmium atoms via the Auger process (immediately after decay of 166Dy). For the pure β 90Sr/ 90Y generator, a 1% release from the DOTA chelator was recorded. On theoretical grounds, an electron ejected with an energy above 0.36MeV (for atomic number=90) is expected to cause recoil of the daughter atom out of a DOTA chelator, if the chemical bond is 3eV. From the β-continuum spectrum of 90Sr, an estimated 10.2% of β particles have an energy exceeding 0.36MeV. For the 166Dy/ 166Ho generator, the matching ratio of experimental release versus Auger transition is explained by the fragmentation of the chelator by Auger electron thereby releasing the holmium atoms. For the 90Sr/ 90Y generator, the calculated and measured percentage release is in the same order of magnitude, proving the equation suitable to describe the classical recoil effect for pure β emission. The discrepancy between the experimental and theoretically calculated release can be explained by a correction of the chemical bond energy to 4.4eV.

Original languageEnglish
Pages (from-to)115-119
Number of pages5
JournalJournal of Labelled Compounds and Radiopharmaceuticals
Volume55
Issue number3
DOIs
Publication statusPublished - Mar 1 2012

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Keywords

  • Dy/ Ho
  • Pd/ Rh
  • Sr/ Y
  • in vivo generators

ASJC Scopus subject areas

  • Analytical Chemistry
  • Biochemistry
  • Radiology Nuclear Medicine and imaging
  • Drug Discovery
  • Spectroscopy
  • Organic Chemistry

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